In recent years, upon shooting of a still image or moving image, image pickup while observing an object image formed on image-pickup pixels in a real-time manner, i.e., live-view image pickup, is desired, and its usage has become popular. Upon live-view image pickup, automatic focus detection is performed by the following two methods. One method is active focusing using an external optical system for light projection and light reception. In this method, light projected on an object is received, and the distance from the object is determined from the positional relation of an image formed with the received light. The other method is contrast detection, in which a contrast change with respect to a focus change in an image-pickup optical system is detected in an object image subjected to photoelectric conversion with image-pickup pixels to determine the focus status.
In the active focusing method, it is impossible to perform focusing on an object in a remote position. In the contrast detection method, as a focus position is detected during focusing, it is impossible to quickly drive a focus lens.
Further, as a method for more quick and accurate focus position detection, Japanese Patent Laid-Open No. 60-125814 proposes a combination of a blur-detecting focus detection mechanism and a phase-difference detecting focus detection mechanism.
However, in the technique disclosed in Japanese Patent Laid-Open No. 60-125814, because a part of an object light ray incident on an image sensor is separated and taken into the focus detection mechanism for the purpose of focus position detection, the image-pickup light ray is attenuated.
Accordingly, Japanese Patent Laid-Open No. 2004-191629 proposes an image pickup device using an image sensor having a phase-difference detection focus detection structure which does not require separation of the object light ray. Japanese Patent Laid-Open No. 2004-191629 discloses, in the phase-difference detection focus detection structure on the above-described image sensor plane, correcting the result of focus detection using ray vignetting information of an image-pickup optical system, so as to acquire focusing accuracy.
A ray vignetting status changes in accordance with zoom position or focus position of the image-pickup optical system. To acquire accurate ray vignetting information, it is necessary to grasp the status of the image-pickup optical system. However, some replaceable photographic optical systems are manufactured without consideration of the phase difference detection on the image sensor plane.